Stopping apparatus for alternating-current motors



H. F. STRATTON.

STOPPING APPARATUS FOR ALTERNATING CURRENT MOTORS.

APPLICATION FILED JULY 12, 199- 1 ,364,84.7. Patented Jan. 4, 1921.

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HARRY F. STRATTON, OF CLEVELAND, OHIO, ASSIGN'OR TO THE ELECTRIC CON-TROLLER & MANUFACTURING COMPANY, OF CLEVELAND,

'IION or 01110.

OHIO, A. CORPORA- STOIPPING APPARATUS FOR ALTERNATING-CURRENT MOTORS.

Specification of Letters Patent.

Patented Jan. 4, 1921.

Application filed July 12, 1919. Serial No. 310,369.

To all whom it may concern Be it known that I, HARRY F. STRATTON, acitizen of the United States, residing at Cleveland, in the county ofCuyahoga and State of Ohio, have invented new and useful Improvements inStopping Apparatus for Alternating-Current Motors, of which thefollowing is a specification.

This invention relates to apparatus for stopping motors, particularly ofthe alternating current type.

The principal ob ectof this invention is to secure the quick stopping ofalternating current or induction motors with the same facility as is nowpossible with direct current motors provided with a controller designedfor reversal and quick stop by dry braking. Other. objects appearhereinafter.

On the accompanying drawings, Figure 1 is a diagrammatic viewillustrative of one of the many ways for carrying out my invention; Fig.2, a section of a detail involving a magnet and clutch, shown on Fig. 1;and Fig. 3, a diagrammatic view of a second form of my invention inwhich the said magnet is not employed. Fig. 4 is a view showing aportion of my invention modified.

Referring first to Figs. 1 and 2, C represents a controller having thecontact fingers 1 to 7 arranged to be engaged by the contact stripsshown at their left. The motor M has the stator windings S and the rotorR. The rotor shaft '1' carries the double-armed contact device loosethereon and seated between the collar c pinned to the shaft and themagnet on havin its casing or frame keyed to the shaft. he casingcontains the magnet-winding w concentric with the shaft and inclosingthe coiled spring a which has one end seated on the bottom of the casingand the other end bearing on the disk (Z loose on the shaft and arrangedandadapted to engage the hub of the contact device r when the expansionof the spring is allowed and causes the said device to rotate with theshaft. The device 8 has two insulated contact arms I) and 0, arranged toengage simultaneously the contacts e, f, or the contacts respectivelywith the contact-finger 2, the contactfinger 4, and the stator terminalz. The contact-finger 1 is'connected to the terminal j of the winding ofthe magnet m, the other terminal is of the magnet being connected to thesupply line L The contactfinger 3 is connected to the stator terminal n;the contact-finger 5 to the stator terminal 0, and to the contacts 6 andh, the contactfinger 6, to the contact arm I); and the contact-finger 7,to the contact arm 0. The contacts e and 72, are connected together, andthe contacts 7 and g are also connected together.

W hen the forward contact strips 8 to 12 are moved by the controller Ginto contact with the contact-fingers 1 to 5, the rotor R will rotate inthe forward direction which will be assumed to be indicated by the arrowp. The line L is connected through the contact-fingers 2 and 3, and thecontact-strips 9 and 10 to the stator terminal a; the line L isconnected through the contact-fingers 4 and 5, and the contact-strips 11and 12 to the stator terminal 0 and to thejcontact e,- and the line L isconnected directly to the stator terminal 71. connected through thecontact fingers 1 and 2, and the contact strips 8 and 9 to the terminalsof the magnet m, which causes' the magnet to pull the disk d towardthe'casing, thereby compressing the spring a, and allowing thecontact-devices to be loose on the shaft 1". It can do no harm, however,if the device is carried over so as to bring the arms 6 and 0 againstthe contacts 0 and f,

as the arms are open circuited on the fingers 6 and 7.

If the reverse contact strips 13 to 17 are brought into engagement withthe fingers 1 to 5, the direction of rotation of the rotor will bereversed as indicated by the arrow 9 the former connections of the linesL and l with the rotor terminals n and 0 being now reversed. The magnetwinding a is energized by current flowing between the lines L and L byway of the fingers 1 and 2, and the strips 13 and 14. No harm can come,if the arms I) and c engage the contacts g and h, as the fingers 6 and 7are still unenergized.

from the forward position into engagement with the fingers 2, 4:, 6, and7, the magnet circuit is opened at the finger 1, and the spring a pushesthe disk (i into contact with the hub of the device 8 and causes thelatter to be clamped to the shaft 1* through friction with the collar 0and the disk 03. The device 8 is rotated with the drifting shaft, itsarms I) and c soon engaging the contacts e and f, if they have notalready done so. Current from the line L passes through the finger 2,the strips 18 and 20, the finger 6, the arm 6, and the contact 6 to therotor terminal 0 and current from the line L passes through the finger4, the strips 19 and 21, the finger 7, the arm 0, and the contacts f andg to the rotor terminal n. The lines L and L being now connected in thereverse order to the rotor terminals n and 0 from what they were whenthe controller was in the forward position, the torque exerted by therotor is now reversed, tending to stop it. The result is that the rotoris quickly brought to rest and even rotates in the reverse direction aslight fraction of a revolution until the connections are broken betweenthe arms 25 and 0, and the contacts 6 and f. The rotor necessarilyactually comes to a standstill be fore it is reversed, .and obviously,it has attained only a very slow speed in the reverse direction when itscircuit is interrupted. The result is that all the torque tending torotate the rotor is removed when the rotor is revolving at very lowvelocity, and consequently, the rotor comes to rest almost immediately.In actual operation this result cannot be distinguished by the eye fromthat of bringing the rotating element to standstill without any reverseof rotation.

One of the principal advantages of thus stopping the motor lies in thedifliculty of disconnecting the motor current by means of any relayaction responsive to motor cur rent, inasmuch as the variation of motorcurrent is very small as the direction of rotation reverses.

If the controller has been brought from the reverse position to the stopposition, the shaft 1 would have carried the arms Z2 and 0 against thecontacts-g and h whereupon the line L would be connected to the rotorterminal n, and the line L to the rotor terminal 0, thereby causing themotor to run in the forward direction and the motor circuit to be atonce opened at the contacts 9 and h, and the motor to be quicklystopped.

In Fig. 3, the parts are the same as in Fig. 1 except. that the magnethas been omitted together with the finger 1 and the strips 8 and 13. Thecontact device 8' is clamped to the shaft 1 in any convenient manner soas to cause it to rotate with the shaft and still allow it to standstill when it engages the stop t or the stop u. When the device isagainst the stop If, its insulated contact arms 6 and 0 engage thecontacts 6 and f; and when it is against the stop u, these-arms engagethe contacts 9 and h.

The device 8 has a slot 11, providing the arm w opposite the arm I). Thebolt as extends through the arms Z) and w, and has thereon the spring yseated between the arm w and the nut 2 on the bolt to draw the arms I;and w toward each other and cause the device 8 to "yieldingly grip theshaftr.

The operation of the apparatus of Fig. 3 is the same as that of Fig. 1,the device 8 gripping the shaft yieldingly all of the time instead of atthe motor is to be stopped.

In Fig. 4:, I have shown a centrifugal governor for opening the motorcircuit when the current becomes low. It may open the circuit to serveas a safety device in case the device .9 of Fig. 1 or s of Fig. 3, or anequivalent device fails to operate, or it may open the circuit sli htlybefore the motor starts to reverse. 8n F rotor shaft 7" driving thegovernor shaft 00 by means of the bevel gears 3 The governor balls 2connected to the cylinder 22 rotatable with and slidable on the shaft wcarry the two contact rings 23 and 24. The brushes 25 are inserted inthe wire leading from the contact-finger 6 and bear on the contact-ring23, and the brushes 26 are inserted in the wire leading from thecontactfinger 7 and bearing on the contact-ring 24. As the speed of themotor becomes zero or quite low, the governor balls fall so low as tocause the brushes 25 and 26 to open the motor circuit.

I have shown the motor connected to a three-phase alternating-currentcircuit without the interposition of a transformer or resistance. If aninduction motor is thrown across the line, the starting current is aboutfive times full load current. If the connections are changed to reversethe motor when running at full speed, the reversing current is onlyabout 10% more than the current taken when startin from rest. Thispermits reversing small mduction motors without the use of a transformeror a resistance, when it is satisfactory to start such a motor byinitially applying full line voltage.

It is to be understood that, although I have given a theory of operationof my device, 1' .do not limit myself to the same, as the principle ofthis invention may be worked out in apparatus and operations differinfrom those set forth herein.

I c aim:

The combination of a reversing motor, forward and reverse circuitstherefor, a selective switch operated by the motor to close a set ofcontacts in the reverse circuit when time only when the ig. 4, I showthe" the motor is operatingin the forward direction and to closeanother. set of contacts in the forward circuit when the motor isoperating in the reverse direction, a master switch having contacts foroperating the.

motor in the forward direction, contacts for operating the motor in thereverse dlrec-

